Gas mantle technology

ABSTRACT

A mechanically durable, highly luminous mantle for a gas-powered light source.

This invention relates to gas mantle technology.

Incandescent mantles have been prepared by impregnating yarns or sleevesof rayon or other organic fiber with a thorium containing compound, andburning off the organic fiber to produce a thoria mantle. Such gasmantles are typically heated to incandescent temperature by a gas flameand provide effective light sources. It is well known that such mantlesare extremely fragile and subject to destruction or damage by accidentaljarring or other relatively mild stresses.

In accordance with one aspect, the invention provides an improved gasmantle structure composed substantially entirely of fibers of oxides ofone or more of the metals thorium, zirconium, yttrium, hafnium,aluminum, magnesium, calcium, cerium and other rare earth metals, andthat have substantially greater shock load resistance than priormantles. While such mantle shock resistance is a function of factorssuch as mantle size, shape, mechanical construction (yarn size, type ofweave, open area, etc.) and mantle support, a useful shock resistancefigure of merit for a cantilever supported mantle whose length anddiameter dimensions are similar is provided, to a first orderapproximation, by the product of the shock load (in g's) that the mantlewithstands and the unsupported length (in meters) of the mantle. Mantlestructures in accordance with this aspect of the invention preferablyhave a shock resistance figure of merit of at least three g-meters andwithstand shock loads in excess of 600 g's.

Preferred gas mantle structures are composed of oxides of a rare earthmetal, hafnium, thorium, yttrium or zirconium as a host, oxides of oneor more rare earth metals different from the host metal as a radiationmodifying dopant, and oxides of one or more metals different from thehost metal such as aluminum, beryllium, magnesium, calcium, yttrium orzirconium as a strengthening dopant. A particular gas mantle structureincludes a self-supporting fabric of metal oxide fibers that distortelastically in a configuration that includes a dome portion that definesa volume of about 0.1 cubic centimeter with a skirt portion that isshrink secured to a ceramic support tube, the mantle fabric beingcomposed essentially entirely of thoria, with about two weight percentceria and about one weight percent alumina. The metal oxide fibers ofthat mantle, after heating in an isobutane flame, have a microstructurewith a significant number of grains of dimensions in the order of one totwo micrometers, and well-delineated grain boundaries, and are efficientin converting thermal energy to radiant energy. The flexibility, orability of the mantle fabric to undergo considerable elastic distortionwithout fracture, is evidence of the high strength of this improvedmaterial.

In preferred mantles, the fabric is knitted in such a way that the yarnyields a self-supporting dome of metal oxide fibers which is heated toincandescence by a gas flame. This dome of metal oxide fibers can bedistorted to a large degree by an external force; in such distortion theyarn filaments bend or twist elastically, and when the force is removedthey regain their original shape, restoring the initial configuration ofthe mantle. Mantles in accordance with this aspect of the invention areable to undergo much larger elastic distortions without fracture thanmantles of similar weaves or knits prepared by conventional methods.

The elementary metal oxide fibers of preferred mantles have across-sectional dimension of less than ten micrometers (approximatelyone third the cross-sectional dimension of the precursor organic fiber),the mantle fabric has greater than fifty percent open area, and, in thedome configuration that defines a volume of about 0.1 cubic centimeterand with a skirt portion that is shrink secured to a heat-resistantsupport tube, the mantle withstands shock loads in excess of six hundredg's. The shock load is the force experienced by the unsupported mantlebecause of rapid deceleration on impact of the support tube against astop. This load is often expressed in g's, where g is the accelerationdue to gravity. Thus, impact loads can involve deceleration forcessubstantially in excess of the force of gravity. As indicated above,mantles in accordance with the invention preferably have shockresistance figures of merit (as above defined) greater than threeg-meters.

While such mantles are useful in a variety of devices, they areparticularly useful in portable light sources of the flashlight typewhich in accordance with another aspect of the invention have a handleportion sized to be grasped in a hand, a supply of fuel (preferably aliquid hydrocarbon such as isobutane, propane, gasoline or the like) inthe handle portion, and a head portion in which the mantle is mounted atthe focus of reflector structure for forming light emitted from themantle into a beam. A fuel supply conduit interconnects the fuel supplyand the mantle, the flashlight also includes a fuel control forcontrolling the flow of fuel through the conduit to the mantle and anigniter mechanism for igniting the fuel to produce flame and cause themantle to emit light. Preferably, light sources in accordance with thisaspect of the invention have wattage ratings of less than fifty watts;include thoria mantles that have been heated to at least 1500° C.; andhave luminous efficiencies of at least about one-half lumen per watt. Ina particular embodiment the liquid fuel is isobutane and interposed inthe conduit is a pressure regulator for supplying fuel at a pressure ofless than 3 psi and an aspirator mechanism for supplying an air fuelmixture to the mantle at approximately stoichiometric ratio. The fuel(vapor) flow rate (at STP) is about seven cubic centimeters per minute,the wattage rating is about fourteen, and the efficiency is about onelumen per watt.

In accordance with another aspect, there is provided an improved processfor producing a sturdy refractory metal oxide article which includes thesteps of heating a substrate of organic material impregnated with ametal compound to increase at a controlled rate the temperature of theimpregnated substrate to a temperature sufficiently high to thermallydecompose the metal compound as a step in the conversion of the metalcompound to a refractory metal oxide; further heating the impregnatedsubstrate to decompose and remove the organic material from theimpregnated substrate and to complete the conversion of the metalcompound to the refractory metal oxide so that a metal oxide replica ofthe substrate remains; and further heating the metal oxide replica tosinter and densify the metal oxide replica such that the densified metaloxide replica has a strength (shock resistance) figure of merit of atleast three g-meters, which strength is retained after the replica hasbeen heated to 1500° C., the resulting metal oxide article in the abovedescribed configuration being capable of withstanding shock forces of atleast about 300 g's, in contrast with more fragile prior art metal oxidereplica structures. The exact choice of reaction conditions depends onthe shape and chemical composition of the starting organic material andon the metal compound or metal compounds employed in the impregnationstep. A preferred organic material for use in the process for producingmetal oxide articles of the invention is low twist rayon yarn. However,other absorbant materials that absorb adequate amounts of the imbibingsolution and that thermally decompose without melting, such as cotton,wool, silk, and certain synthetic materials may also be used The metalcompound and organic substrate material have interaction characteristicssuch that (in a suitable processing sequence in accordance with theinvention) the metal compound undergoes thermal conversion to a skeletalsubstrate replica (with healable fissures or rifts) before thermaldecomposition of the organic material is completed, the furtherresulting gaseous decomposition products being removed from the replicathrough the rifts. A preferred metal compound is a nitrate, but othercompounds may also be used. The metal compound can be impregnated intothe organic material (uniformly distributed within the fibrils) by anyof several methods. Articles of various configurations may be formed inaccordance with the invention, such metal oxide articles having a numberof uses in addition to use as gas mantles.

In a preferred process, the absorbant substrate is a fabric, forexample, a tubular sleeve that is knitted from continuous multi-filament(40-60 filaments of about 17-20 micrometers diameter) low twist, lowtenacity (highly reticulated) viscose rayon yarn of about 150 denier toproduce a fabric with greater than 50 percent open area. This fabricsubstrate is imbibed in an aqueous solution of nitrate salts, theimbibed substrate having a white color and a shiny texture.

The imbibed fabric substrate is then thermally processed undercontrolled conditions. Initially, the temperature of the substrate isgradually increased in an atmosphere with little or no oxygen present(preferably an oxygen partial pressure of less than two mm Hg). When atemperature of 130° C. to 170° C. is reached, a quite vigorous reactionoccurs, involving an interaction between the nitrate salts and thecellulosic substrate, which is visually evidenced by a color change thatstarts at some location in the substrate and produces a front whichseparates a tan color from the shiny white color and advances throughthe substrate in a few seconds This reaction is termed a "nitrate burn"and involves a partial oxidation of the cellulose of the substrate bythe decomposition products of the nitrate ions - the gases produced bythe thermal decomposition of the nitrate salts being strongly oxidizingand reacting with the cellulose. The complex reaction evolves heat and alarge amount of gas (including carbon monoxide and oxides of nitrogen),the evolved carbon monoxide being evidence that a combustion reactionoccurred. Differential scanning calorimeter data shows this reaction tobe rapid and exothermic Rapid denitration appears important to thesubsequent formation of mantles that are strong after heating to 1600°C. and above.

After the nitrate burn, the substrate is heated in an atmosphere thatcontains an increased amount of oxygen (preferably an oxygen partialpressure greater than twenty mm Hg) during which the remaining celluloseis pyrolyzed and the residual carbon is removed by oxidation. Duringthis continued heating, there is some evidence that an intermediatecompound (which may be thorium oxynitrite (ThO (NO₂)₂)) is formed, thegas evolution slows, but continues to about 475° C. where the replica isthorium dioxide. The temperature is further increased to sinter anddensify the metal oxide particles. Beneficial sintering anddensification of the metal oxide replica continue to occur untiltemperatures of at least about 1500° C. are reached. The resulting metaloxide product has a strength that is substantially greater than thestrength of prior art metal oxide products of similar configuration.

Without intending to be bound by the same, the theory and mechanism ofthis process appear to be as follows: When a fabric of organic polymericmaterial, such as cellulose, is immersed in an aqueous solution of ametal compound, it swells and the dissolved metal compound enters theswollen regions. Upon drying, the metal compound in the fibers iseffectively suspended and separated as small islands. The heating of theimpregnated organic material under controlled conditions converts themetal compound to an oxide structure that is a replica of the organicfabric material, the oxide fibers of the replica structure havinghealable rifts or fissures. Gaseous products which are evolved uponfurther thermal decomposition of the organic material are releasedthrough the healable fissures without significant impairment of theoxide replica. Further heating of the replica to higher temperaturesincreases the strength of the replica. It is believed that this healingand strengthening action involves solid state diffusion which blunts orrounds the roots of the crack-like fissures or rifts, thus reducingtheir severity. In some cases, the rifts may heal entirely.

In particular processes, the fabric is imbibed in an aqueous solution ofnitrate salts that have a molar concentration of less than 1.4,preferably in the range of 0.7-1.0 molar, particular compositionscontaining thorium nitrate, cerium nitrate and aluminum nitrate inconcentrations such that the final sintered product contains ceria inthe amount of 0.5-3.0 weight percent and alumina in the amount of0.1-2.0 weight percent, and a particular composition having about twopercent by weight cerium oxide and about one percent by weight aluminumoxide in the final sintered product. The rayon fabric sleeve is imbibedin the metal nitrate solution at about 20° C. for about ten minutes, andthen is centrifuged to remove excess solution from the surface of thefibers.

The impregnated organic fiber sleeve is then shaped with the use of ashaping form into the desired configuration, in a particular case amantle sock, and then dried. The shaped impregnated dried fabric sock isthen positioned on a support post of a processing fixture with the socksurrounding a tube of heat-resistant material such as stainless steel orceramic carried on the support post and with the closed end of the sockspaced a predetermined distance above the upper end of the tube; andthermally processed under controlled conditions as described above toinitiate conversion of the metal nitrates to metal oxides in adenitration step, then to complete the decomposition of the rayon fibersand the conversion to metal oxide, the resulting gases being evolvedthrough the fissures without impairing the healability characteristicsof fissure-type defects in the metal oxide, and then to heat theresulting metal oxide fabric replica to temperatures of at least about1000° C. to sinter and densify the metal oxide particles. In onepreferred product, the resulting metal oxide mantle is composedessentially entirely of thoria, ceria and alumina.

The following processes for producing thorium oxide fibers fromimpregnated cellulosic fibers employ examples of preferred reactionconditions. In each process, an open area type of absorbant cellulosicsubstrate is impregnated by immersing it in an aqueous solution ofthorium nitrate. Excess solution is then carefully removed and theimpregnated substrate is formed (if desired) and dried. In a firstprocess, the denitration step is carried out by heating the impregnatedsubstrate in a flowing inert gas atmoshhere while raising thetemperature at a uniform rate (preferably at least 2° C. per minute)from room temperature to 320° C. during which interval denitrationoccurs (approximately at 150° C.); then an oxygen flow (about threepercent of the nitrogen flow) is added and the chamber temperature isheld at 320° C. for a soaking interval during which time the cellulosicsubstrate pyrolyses and oxidizes until no visual evidence of residualcarbon remains; at the end of that soaking interval the oxygen flow isincreased to about twenty-five percent of the nitrogen flow and thechamber temperature is rapidly increased to 900° C. to sinter anddensify the metal oxide particles; and then the resulting porous thoriastructure is heated to a temperature of about 1600° C. in an isobutaneflame for about five minutes for further thoria particle sintering anddensification.

In a second process, the denitration step is carried out by heating animpregnated porous fabric sleeve in a low pressure environment, thetemperature being gradually increased from 100° C. to 200° C. over aninterval of about twenty minutes during which interval denitrationoccurs; the denitrated fabric is then heated in an air atmosphere withtemperature gradually increased from 240° C. to 450° C. over an intervalof about one hour during which interval the rayon fabric is pyrolysedand the residual carbon is removed by oxidization; the resulting metaloxide replica is then heated at a temperature of about 1000° C. for tenminutes; and finally the metal oxide replica is heated at a temperatureof about 1600° C. for five minutes.

Metal oxide fabrics of the invention, in visual appearance,substantially retain characteristic physical textile attributes of theirprecursor organic fabrics, although they are substantially reduced indimension. Those metal oxide fabrics are characterized by relativelyhigh density, strength (preferrably a shock resistance figure of meritof at least three g-meters) and flexibility, and in preferred mantleconfigurations are efficient radiation sources (a luminous efficiency ofat least one-half lumen per watt and an output of at least ten lumenswith a one gram per hour isobutane flow rate) and withstand impact loadsof several hundred g's.

Other features and advantages will be seen as the following descriptionof particular embodiments progresses, in conjunction with the drawings,in which:

FIG. 1 is a diagrammatic view of a portable light source of theflashlight type in accordance with aspects of the invention;

FIG. 2 is an enlarged view of the mantle and its support employed in theflashlight of FIG. 1;

FIG. 3 is a view of a portion of a fixture used in the manufacture ofthe mantle shown in FIG. 2;

FIGS. 4 and 5 are graphs indicating particular processing sequences forthe manufacture of mantles in accordance with the invention.

DESCRIPTION OF PARTICULAR EMBODIMENTS

Shown in FIG. 1 is a flashlight 10 that has a handle portion 12 and ahead portion 14. Disposed in handle 12 is a container 16 of isobutanefuel--a charge of twenty grams with an equilibrium vapor pressure atroom temperature of thirty psi--together with pressure regulator 20 toprovide two psi fuel pressure at regulator outlet orifice (0.05millimeter diameter). Valve 18 controls the flow of gas throughregulator 20 and venturi 22 (that has a throat of about one millimeterdiameter and provides an air fuel ratio of about 30:1) to support tube28 which carries metal oxide fiber mantle 30. Reflector 32 directsradiation from mantle 30 in a collimated beam of light through lens 34.Control switch 36 operates valve 20 to provide flows of fuel to venturi22 and to pilot tube 38. Igniter 40 includes flint wheel 42 or othersuitable igniter such as a piezoelectric device that is operated bylever 44 to ignite pilot fuel which in turn ignites the main flow offuel in mantle 30. The flashlight has a rating of about fourteen watts,consumes fuel at a rate of about one gram per hour (a vapor flow rate ofabout seven cubic centimeters per minute) and has a luminous efficiencyof about one lumen per watt. Further details of the construction of thisflashlight may be had with reference to copending application Ser. No.408,549 filed Aug. 16, 1982 in the names of Walter J. Diederich andGeorge P. Gruner, entitled TWO-STAGE PRESSURE REGULATOR, and assigned tothe same assignee as this application, which application is expresslyincorporated herein by reference.

Further details of mantle 30 and its support tube 28 may be seen withreference to FIG. 2. Support tube 28 is of mullite and has a length ofabout 25 millimeters, an outer diameter of about five millimeters, andan inner diameter of about three millimeters. Mantle 30 is aself-supporting structure of metal oxide fiber fabric that defines ahollow chamber of about seventy cubic millimeters volume with its tip 50about one half centimeter above the upper end surface 52 of support tube28. The skirt 54 of the mantle fabric (about one-half centimeter inlength) is firmly secured (shrink fitted) to the outer surface ofsupport tube 28. The shape of the outer surface of support tube 28 maybe varied to achieve desired mantle configurations, for example a flutedmantle sidewall shape. Auxiliary means such as an inorganic cement 56 ora recess may optionally be used to enhance the securing of mantle 30 totube 28.

The mantle fabric is formed of metal oxide multifilament strands 60 inan open knit array with openings 62 such that the open area of thefabric is about 60%. The cross-sectional dimensions of the individualfibers of strands 60 are in the range of about 5-10 micrometers and thestrands 60 have cross-sectional dimensions in the order of about 0.1millimeter with the openings 62 having dimensions of about 0.5millimeter.

The following is a process for manufacturing mantle 30. Continuous lowtwist, low tenacity (highly reticulated), viscose rayon yarn 60 (150denier/42 filament) is knitted into a continuous tubular sleeve using aLamb circular string knitter (Model ST3A/ZA) with a 7/8 inch diameterarbor and 24 needle capacity using 14 needles in the arbor in thesequence: NNONONONNONONNONONONNONO, where "N" represents a slot filledwith a needle and "0" represents an open slot. The yarn is knitted withtension on both the yarn and the knitted sleeve to attain nine stitchesper linear inch of tensioned sleeve, and the continuous length ofknitted sleeve is wound onto a take-up spool.

An imbibing solution is formed by dissolving (1) hydrated thoriumnitrate (Th(NO₃)₃)₄.4 H₂ O) powder (reagent grade); (2) hydrated ceriumnitrate (Ce(NO₃)₃.6 H₂ O) powder (reagent grade); and (3) hydratedaluminum nitrate (Al(NO₃)₃.9 H₂ O) powder (reagent grade) in distilledwater (together with a small amount of a non-ionic wetting agent such asTriton X-100) to provide a solution 0.8 molar in thorium nitrate, 0.03molar in cerium nitrate and 0.03 molar in aluminum nitrate.

Knitted rayon sleeve units, in lengths of about thirty centimeters, areimmersed for about ten minutes in the imbibing solution at roomtemperature, with optional gentle agitation to promote penetration ofthe imbibing solution into the rayon fibers. After the ten minuteinhibition, the sleeves are removed from the solution, squeeze dried andthen transferred to plastic tubes of a centrifuge. The sleeves are thencentrifuged for ten minutes at about 200 g's to remove surface liquid.It is convenient to secure a metal screen halfway from the bottom ofeach centrifuge tube so that liquid does not rewet the surface of thesleeve during or after centrifugation.

After centrifugation, the imbibed sleeves are formed into mantle sockswith aid of a Teflon sock-shaping rod that is about fourteen millimetersin diameter and has a hemispherical end. Each imbibed sleeve is cut intolengths of about seven centimeters, slipped over the shaping rod, andtied off at the hemispherical end of the shaping rod with a piece oftreated yarn unraveled from the bottom of the knit sleeve. One loop ofyarn is passed around the knit sleeve just above the hemispherical topof the rod and tied with a double overhand knot. The free ends of theyarn and of the sleeve above the knot are cut as short as possible. Theshaped socks 70 are then dried with a flow of hot (about 90° C.) air,slipped off the shaping rods, cut to lengths of about 3.6 centimeters,and then hung on a fixture that includes mullite base 72 and a series ofupstanding mullite posts 74 (spaced at about three centimeter intervalson base 72. Each post 74 has a diameter of about 3 millimeters and alength of about 3.7 centimeter and receives a support tube 28 and spacer76 as indicated in FIG. 3, the top of tube 28 being spaced about fivemillimeters below the top of post 74. Optionally a ring 78 of sodiumsilicate that has been pretreated by heating tube 28 to about 900° C.may be carried by tube 28 as indicated in FIG. 3.

The fixture with knitted imbibed socks 70 hung over the support sleeves28 on the fixture posts 74 is then subjected to a firing procedure toconvert the metal nitrate imbibed cellulosic mantle socks into lightemitting and mechanically strong metal oxide mantles.

In the processing sequence illustrated in FIG. 4, the fixture with socks70 is placed in a tubular oven that is about 1.2 meters in length andabout five centimeters in inner diameter. At ambient temperature (about25° C. (point 80)), the oven is flushed with tank nitrogen at a flowrate of 200 cubic centimeters per minute (a flow velocity of about tencentimeters per minute), and with this inert atmosphere in the oven, theoven temperature is increased at a rate of four degrees Celsius perminute as indicated at line 82. The mantle fabric 70 undergoesdenitration at about 150° C. (point 84). At this point the fabric colorchanges rapidly from white to golden tan. Immediately after this colorchange (point 84), oxygen is added to the nitrogen flow at a rate ofabout five cubic centimeters per minute. Heating continues at the samerate as indicated by line 86 to a temperature of about 320° C. (point88). During this time the color continuously changes from golden tan todark brown or black with modest shrinkage (about 10%) of the fabric,which indicates additional decomposition of the organic material.Continuing from point 88, the oven temperature is then held at about320° C. for as long as it takes the mantles to turn from black to lightgray or white (about two hours). During this soaking interval (indicatedby line 90 in FIG. 4), the remaining carbon is oxidized and driven offand the mantle shrinks to about 1/3 its original dimensions with itsskirt portion 54 shrunk onto sleeve 28 essentially as shown in FIG. 2.At the end of the soaking interval, (at point 92) the flow of oxygen isincreased to fifty cubic centimeters per minute (a gas mixture of 20%oxygen) and the oven temperature is rapidly increased as indicated atline 94 to a temperature of 900° C. (point 96). The heater is thenturned off and the oven cools to ambient temperature as indicated at 98.

After cooling, each mantle subassembly is removed from its storageholder post 74 and is optionally exposed to a burning mixture ofisobutane and air (at an estimated temperature of about 1600° C.) forfive minutes to further shrink and densify the metal oxide fabric.

The mantle 30 with its support tube 28 is evaluated for shock strengthIn one test mechanism, the mantle-support tube assembly is secured to a1/4 pound weight with a set screw in either a vertical or a horizontalorientation. The weight slides on a six foot vertical steel rod thatpasses through a hole in the 1/4 pound weight and, at the bottom of thesteel rod, the weight impinges on a spring that has a force constant of810 pounds per inch A drop height of six feet represents a shock load ofabout 620 g's, a drop height of five feet represents a shock load ofabout 570 g's, a drop height of about four feet represents a shock loadof about 510 g's, and a drop height of three feet represents a shockload of about 445 g's. Mantles have also been tested with a L A BAutomatic Drop Shock Tester (Model SD-10-66-30) (available from MaterialTechnology Incorporated) which is used with a Type 5520.5.85Decelerating Device (pulse pad) for shock loads of up to about 600 g'sand with a Type 5520.5.28 Decelerating Device (pulse pad) for shockloads in the range of 600 g's to 1600 g's. The following is a summary ofresults of such tests on mantles in accordance with the invention:

    ______________________________________                                        STRENGTH OF MANTLES                                                           Mantle  Mantle   Average   Range of                                           Diameter                                                                              Length   Fracture  Fracture Figure of                                 (D)     (L)      Load      Loads    Merit                                     (mm)    (mm)     (g's)     (g's)    (g-meters)                                ______________________________________                                        5       6        983       800-1600 5.9                                       ______________________________________                                    

In contrast, prior art Valor (German Railway) mantle subassemblies (9 mmmantle diameter and 8 mm mantle length) tested with the LAB Testerfailed at average fracture loads of 152 g (78-280 range)--a figure ofmerit value of 1.2 g-meters; and prior art Coleman mantle subassemblies(25 mm mantle diameter and 28 mm mantle length) failed at averagefracture loads of 80 g (60-90 g range)--a figure of merit of 2.2g-meters

The mantle-support tube subassembly is installed in the flashlight 10.With a fuel flow of nine cubic centimeters per minute and a roughlystoichiometric air fuel ratio, the flashlight has a light output in therange of 15-19 lumens.

A second processing sequence is illustrated in FIG. 5. Fixture 72 withhanging imbibed socks 70 is placed in a vacuum oven (preheated toapproximately to 100° C. - point 100) and the oven is pumped down with amechanical vacuum pump over an interval of about five minutes to apressure of five millimeters of mercury (interval 102--FIG. 5). Thetemperature of the oven is then increased at a rate of about fivedegrees Celsius per minute as indicated at 104 for an interval of abouttwenty minutes to a temperature of 200° C. (point 106). Denitration isobserved below 200° C. by a sudden vigorous charring wave thatpropagates over the entire surface of the mantle socks 70.

Immediately after denitration, the support 72 with denitrated socks 70is transferred to an air oven (Kerr Sybron model 999) preheated to 240°C. (point 108). The oven temperature is increased at a rate of about1.7° C. per minute interval 110) to a temperature of about 320° C.(point 112) and then at a rate of about 2.7° C. per minute (interval114) to a temperature of 450° C. (point 116)). Heating to 320° C. andabove causes a continual charring and shrinkage of the mantle until atabout 400° C. to 420° C., the charred portion is oxidized to leave ashrunken mantle of white metal oxide. The mantle support fixture 72 isthen transferred to an air furnace maintained at 1000° (point 118), andafter a ten minute interval (120) the mantle fixture 72 with white metaloxide mantles 30 shrunken on support tubes 28 are removed from thefurnace. Each mantle subassembly is then exposed to a temperature ofabout 1600° C. for five minutes to further shrink and densify the metaloxide fabric. The resulting mantle subassemblies have shock resistancefigures of merit of over 3.6 g-meters and withstand shock loads of over600 g's.

The support tube-mantle subassembly is assembled into the flashlightunit 10 as indicated in FIG. 1. In that assembly, the flashlight has anoutput of about twelve lumens with a butane fuel flow rate of sevencubic centimeters/minute and an air fuel ratio of about 30:1. Theflashlight 10 has an operating life of about twenty hours continuousoperation.

Another mantle support tube subassembly in accordance with theinvention, formed with an imbibing solution about 0.89 molar in thoriumnitrate, 0.01 molar in cerium nitrate and 0.02 molar in zirconium andprocessed after denitration with a sequence that included a twenty-fourhour soaking interval at 320° C. and final heating in a gas-oxygenflame, withstood a shock load of 850 g (a shock resistance figure ofmerit of about 5.0). Still another mantle support tube subassembly inaccordance with the invention, formed with an imbibing solution about0.89 molar in thorium nitrate, 0.01 molar in cerium nitrate and 0.01molar in aluminum nitrate and processed after denitration with asequence that included a twenty-four hour soaking interval at 300° C.and final heating in an isobutane flame, withstood a shock load of 910 g(a shock resistance figure of merit of about 5.5 g-meters).

While particular embodiments of the invention have been shown anddescribed, various modifications will be apparent to those skilled inthe art, and therefore it is not intended that the invention be limitedto the disclosed embodiments or to details thereof, and departures maybe made therefrom within the spirit and scope of the invention.

What is claimed is:
 1. A light source comprisinga fuel supply, a fuelsupply conduit connected to said fuel supply and having an outlet port,a self-supporting metal oxide fiber mantle supported on said fuel supplyconduit adjacent said outlet port, the subassembly of said conduit andsaid mantle having a strength (shock resistance) figure of merit of atleast three g-meters, and said mantle retains such strength after saidmantle has been heated to a temperature of 1500° C., a fuel control forcontrolling the flow of fuel to said mantle through said conduit, and anigniter mechanism for igniting said fuel to cause said mantle to becomeincandescant and emit light, said light source having a luminousefficiency of at least about one-half lumen per watt.
 2. The source ofclaim 1 wherein said source has an output of at least ten lumens with anisobutane fuel flow rate of one gram per hour, a wattage rating of lessthan fifty watts, and said mantle has strength to withstand impact loadsin excess of 300 g's without failure.
 3. The source of claim 2 whereinsaid source has a handle portion sized to be grasped in a hand, and saidfuel supply is in said handle portion.
 4. The source of claim 3 whereinsaid self-supporting metal oxide fiber mantle is composed of metal oxidestrands that have a cross-sectional dimension in the order of 0.1millimeter and said mantle has an open area in excess of fifty percent.5. The source of claim 4 wherein said metal oxide strands aremulti-filament, each said filament having a cross-sectional dimension inthe order of ten micrometers.
 6. The source of claim 1 wherein saidself-supporting metal oxide fiber mantle has an overall length of aboutone half centimeter and a diameter of about one half centimeter.
 7. Thesource of claim 1 wherein said self-supporting metal oxide fiber mantleis shrink-supported on said fuel supply conduit.
 8. The source of claim1 wherein said fuel is a liquid hydrocarbon such as isobutane, propane,gasoline or the like.
 9. The source of claim 1 and further including apressure regulator connected in said conduit between said fuel supplyand said outlet for supplying fuel to said outlet at a pressure of lessthan three psi.
 10. The source of claim 1 and further including anaspirator mechanism for supplying an air-fuel mixture in approximatelystoichiometric ratio connected in said conduit between said fuel supplyand said outlet.
 11. The source of claim 7 wherein said mantle iscomposed of interlocked metal oxide fibers, each said fiber being aboutseven micrometers in diameter, a significant portion of the crystallitesof said fibers being greater than one micrometer in size.
 12. The sourceof claim 11 wherein said fibers of said mantle are composed of theoxides of a host metal selected from the class of zirconium, yttrium,thorium, hafnium and rare earth metals; and at least one dopant metalselected from the class consisting of cerium and other rare earthmetals, aluminum, beryllium, calcium, magnesium, and zirconium, saiddopant metal being different from said host metal.
 13. The source ofclaim 11 and further including a pressure regulator connected in saidconduit between said fuel supply and said outlet for supplying fuel tosaid outlet at a pressure of less than three psi, said liquid fuelsupply in said housing is isobutane, and an aspirator mechanism forsupplying an air-fuel mixture in essentially stoichiometric ratio isconnected in said conduit between said fuel supply and said outlet, saidsource having an output of at least ten lumens with an isobutane fuelflow rate of one gram per hour, a wattage rating of less than fiftywatts, and said mantle having strength to withstand impact loads inexcess of 600 g's without failure.
 14. A sturdy flexible metal oxidearticle composed of the oxide of at least one metal selected from thegroup consisting of thorium, zirconium, hafnium, yttrium, cerium, otherrare earth metals, aluminum, beryllium, calcium, and magnesium,saidmetal oxide being in microcrystalline form with a substantial number ofindividual crystallites having a size in the range of 1-2 micrometersand with well-delineated crystallite boundaries, said microcrystallinestructure being stable at temperatures of 1500° C., and said articlehaving a shock resistance figure of merit of at least three g-meters 15.The article of claim 14 wherein said article is in the form ofinterlocked elongated fibers.
 16. A fabric article composed ofinterlocked metal oxide fibers of claim 15, each said fiber being aboutseven micrometers in diameter, a significant portion of the crystallitesof said fibers being greater than one micrometer in size.
 17. Thearticle of claim 16 wherein said fabric article has strength such thatit withstands deceleration forces in excess of 600 g's without fracture.18. The article of claim 15 wherein said fibers are composed of theoxides of a host metal selected from the class of zirconium, yttrium,thorium, hafnium, and rare earth metals; and at least one dopant metalselected from the class consisting of cerium and other rare earthmetals, aluminum, beryllium, calcium, magnesium, yttrium and zirconium,the dopant metal being different from the host metal.
 19. Aself-supporting metal oxide fiber mantle that defines a hollow spacecomprisingan interconnected array of metal oxide fibers, said fiberarray having an open area of at least fifty percent and having strengthsuch that, when it is secured to a support member, it has a shockresistance figure of merit of at least three g-meters, and said mantleretains such strength after said mantle it has been heated to atemperature of 1500° C.
 20. The mantle of claim 19 wherein said fibersare composed of at least one oxide of a metal selected from the classconsisting of thorium, zirconium, yttrium, hafnium, cerium, and otherrare earth metals, aluminum, beryllium, magnesium, and calcium, saidmantle having strength such that, when it is secured to a supportmember, it withstands deceleration forces in excess of 300 g's withoutfracture.
 21. The mantle of claim 20 wherein said mantle has strengthsuch that it withstands deceleration forces in excess of 600 g's withoutfracture
 22. The mantle of claim 21 wherein said metal oxide fabric isat least ninety-five percent thoria.
 23. The mantle of claim 22 whereinsaid metal oxide fabric further comprises ceria and alumina.
 24. Themantle of claim 23 wherein said ceria is in the amount of 0.5-3.0 weightpercent and said alumina in the amount of 0.1-2.0 weight percent. 25.The mantle of claim 19 wherein said self-supporting metal oxide fibermantle has an integral skirt portion that is shrink-supported on asupport tube.
 26. The mantle of claim 25 wherein said mantle ismechanically secured on said support tube by an inorganic cement. 27.The mantle of claim 26 wherein said inorganic cement is sodium silicate.28. The mantle of claim 20 wherein said metal oxide is inmicrocrystalline form with a substantial number of individualcrystallites having a size in the range of 1-2 micrometers and withwell-delineated crystallite boundaries, said microcrystalline structurebeing stable at temperatures of 1500° C.
 29. The mantle of claim 28wherein said fibers are elongated and interlocked.
 30. The mantle ofclaim 29 wherein each said fiber is about seven micrometers in diameter,a significant portion of the crystallites of said fibers being greaterthan one micrometer in size.
 31. The mantle of claim 30 wherein saidmantle defines a hollow space of less than about 0.2 cubic centimetervolume.
 32. A sturdy refractory metal oxide article comprisinganinterconnected array of metal oxide portions, said article having anopen area of at least fifty percent and having strength such that, whenit is secured to a support member, it has strength to withstand impactloads in excess of 300 g's without failure and a shock resistance figureof merit of at least three g-meters.
 33. The article of claim 32 whereinsaid article has strength such that it withstands deceleration forces inexcess of 600 g's without fracture.
 34. A metal oxide fabric articlecomposed of interlocked fibers of at least one oxide of a metal selectedfrom the class consisting of thorium, zirconium, yttrium, hafnium,cerium, and other rare earth metals, aluminum, beryllium, magnesium, andcalcium, said fabric article having a shock resistance figure of meritof at least three g-meters, and said fabric article retaining suchstrength after said fabric article has been heated to a temperature of1500° C.
 35. The metal oxide fabric article of claim 34 wherein saidmetal oxide fabric article has strength such that, when it is secured toa support member, it withstands deceleration forces in excess of 600 g'swithout fracture.
 36. The metal oxide fabric article of claim 34 whereinsaid metal oxide fabric is at least ninety-five percent thoria.
 37. Thearticle of claim 36 wherein said metal oxide fabric further comprisesceria and alumina.
 38. The article of claim 35 wherein said article is aluminescent mantle that has a luminous efficiency of at least aboutone-half lumen per watt.
 39. The mantle of claim 38 wherein said mantlehas an output of at least ten lumens with an isobutane fuel flow rate ofone gram per hour.
 40. The mantle of claim 39 wherein said metal oxidefibers comprise thoria.
 41. The mantle of claim 40 wherein said metaloxide fibers further comprise ceria and alumina.
 42. The mantle of claim41 wherein said fibers comprises ceria in the amount of less than abouttwo weight percent and alumina in the amount of less than about oneweight percent.
 43. The article of claim 34 wherein said article is aself-supporting metal oxide fiber mantle that has an overall length ofabout one half centimeter and a diameter of about one half centimeter.44. The article of claim 34 wherein said article is a self-supportingmetal oxide fiber mantle that defines a hollow space of less than about0.2 cubic centimeter volume.
 45. The article of claim 44 wherein saidself-supporting metal oxide fiber mantle has an integral skirt portionthat is shrink-supported on a support tube.
 46. The article of claim 45wherein said support tube is of a ceramic material.
 47. The article ofclaim 44 wherein said mantle comprises ceria in the amount of about twoweight percent or less and alumina in the amount of about one weightpercent or less.
 48. The article of claim 45 wherein saidself-supporting metal oxide fiber mantle is mechanically secured on saidsupport tube by an inorganic cement.
 49. The article of claim 48 whereinsaid inorganic cement is sodium silicate.